Carcinogenesis is a process by which normal cells are transformed into cancer cells. It is characterized by a progression of changes at the cellular, genetic, and epigenetic level that ultimately reprogram a cell to undergo uncontrolled cell division, thus mostly forming a malignant mass. Though it is well-established that carcinogenesis is largely the result of irregular activation of oncogenes and/or inactivation of tumor-suppressors, which lead to various pathological changes, the reasons of carcinogenesis are various or not yet known. Furthermore, carcinogenesis pathways involve many genes, factors and conditions, which themselves and their interactions remain very complicated or unclear. Consequently, the development of anti-cancer drugs is simply based on the stroke of luck by trial-and-error, with the society still suffering under the lack of effective anti-cancer medications.
The Kras oncogene was first described in 1983 (McGrath J. P. et al., Nature 304, 501-506 (1983)) and thought to represent a potential drug target. For three decades, there have been many attempts to inhibit pharmacologically its carcinogenic action. Unfortunately, such efforts have so far failed (Watson J. Open Biol 3, 120144 (2013)). In parallel, Myc (formerly “c-Myc”), which acts downstream of Kras and other signaling pathways involved in carcinogenesis (such as Wnt and Notch), was also tested as a potential drug target for new anti-cancer drugs. Myc is functionally important for cellular proliferation, differentiation, apoptosis, and cell cycle progression and is found to be deregulated in many kinds of human tumors (Vita, M. & Henriksson, M. Semin Cancer Biol 16, 318-330 (2006)).
Myc along with Max belong to the basic helix-loop-helix leucin zipper (bHLHZip) protein family (Xu Y., et al., Bioorg Med Chem 14, 2660-2673 (2006)), and Myc can bind DNA only as a dimer with Max, whereby the complex formation activates the expression of many genes. A role of Myc in human cancers, for example, pancreatic ductal adenocarcinoma, was already suggested 20 years ago (Yamada H, et al., Jpn J Cancer Res. 77, 370-375 (1986)). Therefore, inhibition of Myc/Max dimerization has been studied in an attempt to control or modulate the progression of various cancers.
Until recently, Myc was not considered to be a suitable target for drug-treatment. Myc plays an essential role in the proliferation of all normal cells: The concern had been raised that systemic Myc inhibition would trigger devastating side effects, especially in the tissues exhibiting rapid turnover (Soucek, L., et al., Nature 455, 679-683 (2008)). However, experiments with “Omomyc”, a mutant bHLHZip Myc domain of 90 amino acids, which acts in a dominant-negative fashion as a competitive inhibitor of Myc/Max dimerization-dependent transcription by forming a heterodimer with either Myc or Max have shown successful usage of inhibiting Myc/max interaction (Soucek, L., et al., loc. cit.). Systemic inhibition of Myc in mice carrying a conditionally activatable Omomyc construct resulted in mild and tolerable side-effects, while Omomyc action in the lung caused regression of LSL-Kras*-induced non-small-cell adenocarcinomas (Soucek, L., et al., loc. cit.).
Apart from the issue whether Myc represents a possible drug target, inhibition of Myc/Max dimerization has been the subject of research for quite some time, involving small peptides (D'Agnano, I. et al., J Cell Physiol 210, 72-80 (2007)), but also small molecules, which may exhibit an inhibitory effect on this dimerization. For example, Berg, T., et al., (Proc Natl Acad Sci USA 99, 3830-3835 (2002)) reported two small-molecule inhibitors of Myc/Max dimerization. Yin X., et al., reported another four compounds disrupting the association between Myc and Max (Yin X., Oncogene 22, 6151-6159, (2003)). Xu, Y, et al. reported yet another four compounds showing in vitro inhibitory effects on Myc/Max dimerization (Xu Y., et al., Bioorg Med Chem 14, 2660-2673 (2006)). Kiessling et al., further reported five test compounds including Mycro3, some of which exhibited selective Myc/Max dimerization (Kiessling, A., et al., ChemMedChem 2, 627-630 (2007)).
Although there are several in vitro studies on Myc/Max dimerization inhibitors, very few reported in vivo effects of those compounds. The compound 10058-F4 was among the first compounds found to be an inhibitor of Myc/Max dimerization. Gomez-Curet et al. (J Pediatr Surg 41, 207-211 (2006)) reported that 10058-F4 also decreased Myc mRNA levels in lymphoma cells, and inhibited the cell growth in a time- and dose-dependent manner. Huang et al. (Exp Hematol 34, 1480-1489 (2006)) reported that 10058-F4 induced apoptosis and differentiation in primary acute myeloid leukemia cell cultures. Lin et al. (Anticancer Drugs, 18, 161-70 (2007)) showed that 10058-F4 arrested hepatocellular carcinoma cells at G9/G1 phase of the cycle. Sampson et al. (Cancer Res 67, 9762-70 (2007)) reported that 10058-F4 also inhibited Myc protein expression in Burkitt lymphoma cells.
Based on many encouraging in vitro results for 10058-F4, Guo et al. (Cancer Chemother Pharmacol 63, 615-625 (2009)) investigated the preclinical pharmacology in mice bearing human prostate cancer xenografts. However, surprisingly, no significant inhibition of tumor growth in mice was observed after two weeks in vivo treatment with either 20 or 30 mg/kg 10058-F4. The lack of antitumor activity of 10058-F4 in vivo was assumed to be based on its poor pharmacokinetics. Accordingly, this shows the inherent difficulty of predicting in vivo outcome in an animal disease model based on any observed in vitro efficacy.
Hence, there is still a need in the art for efficient therapeutics that can prevent or inhibit tumor growth in mammals, in particular in humans.